Pseudomonic acid A is an antibiotic that has a growth inhibiting effect mainly against Gram positive bacteria (e.g. Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, Klebsiella pneumoniae) and some Gram negative bacteria (e.g. Haemophilus influenzae, Neisseria gonorrhoeae) [A. Ward, D. M. Campoli-Richards, Drugs 32, 425-444 (1986)] and its minimal inhibiting concentration is in the range of 0.02-0.5 mg/dm3. Pseudomonic acid A, by inhibiting the isoleucine-tRNA synthase enzyme, affects the peptide synthesis of pathogen bacteria [J. Hughes and G. Mellows, Biochem. J. 191, 209-219 (1980)]. An advantageous feature of this antibiotic is that it has very low toxicity both for humans and animals and it is negative in the Ames test. Pseudomonic acid A is presently used in human therapy, in various formulations, for the treatment of skin infections (e.g. impetigo, pyoderma), nose and external ear infections, acne, burns, eczema, psoriasis, in case of ulceration for treatment of secondary infections, and for prevention of hospital infections.
The chemical structure of pseudomonic acid A is 9-{4[5S(2S,3S-epoxy-5S-hydroxy-4S-methylhexyl)-3R,4R-dihydroxy-tetrahydropyran-2S-yl]-3-methylbut-2(E)-enoyloxy}nonanoic acid [E. B. Chain and G. Mellows, J. C. S. Chem. Comm. 847-848 (1974); R. G. Alexander, J. P. Clayton, K. Luk, N. H. Rogers, T. J. King, J. C. S. Perkin I. 561-565 (1978)], as depicted by formula (I):

It is known that Pseudomonas fluorescens is able to produce the pseudomonic acid A. According to the British Patent No. 1,395,907, the Pseudomonas fluorescens NCIB 10586 strain is able to biosynthesize the pseudomonic acid complex consisting of pseudomonic acid A and its isomer being a double bond in the cis position between the carbon atoms C2 and C3 and pseudomonic acid B. The ratio of the components is 4.5:4.5:1. According to the Japanese patent application No. 52-70083, however, the Pseudomonas fluorescens Y-11633 strain is able to biosynthesize the pseudomonic acid complex consisting of the pseudomonic acid A, pseudomonic acid B and further two components with unknown structures in the ratio of 9:0.5:0.5.
Mupirocin calcium, an antibiotic derived from pseudomonic acid is currently marketed in the United States as Bactroban®. Bactroban® is recommended for treatment of secondarily infected traumatic skin lesions caused by strains of Stephylococcus aureus and Streptococcus pyogenes. Bactroban® is sold as a topical cream or a nasal ointment and has a calcium salt strength of 2% equivalent base. According to the maker of Bactroban®, mupirocin calcium could be administered orally at 500 mg, and intravenously at 250 mg without any major side effects.
Mupirocin calcium is especially effective against gram-positive bacteria, but may also be used against gram negative bacteria. It inhibits bacterial protein synthesis by irreversibly binding to bacterial isoleucyl transfer-RNA synthetase.
The calcium salt of pseudomonic acid (“mupirocin calcium”) has been disclosed in various patents. U.K. Pat. Nos. 1,577,545 and 1,577,730, incorporated herein by reference, disclose the use of mupirocin calcium in the treatment of diseases. The '545 patent is directed to the treatment and prevention of swine dysentery with the calcium salt of mupirocin. The '730 patent is directed to the use of the calcium salt of mupirocin to treat respiratory, venereal and mycoplasma-induced diseases in non-human mammals. The disclosure focuses on the efficacy of mupirocin as a drug, rather than its preparation.
U.S. Pat. No. 4,879,287 is directed to a pharmaceutical composition of mupirocin calcium for topical administration comprising hydrated crystalline calcium salt, and a corticosteroid. The '287 patent discloses various formulations for crystalline mupirocin calcium and is incorporated herein by reference.
U.S. Pat. Nos. 5,596,672, 5,436,266, 5,191,093 and 4,916,155 (Baker et al.), all within the same family, disclose a crystalline calcium salt of mupirocin, and claim its composition, method of preparation and administration. All these patents are incorporated herein by reference. The '672 patent is directed to a method of treating bacterial infections with crystalline mupirocin calcium or a hydrate thereof. The '266 patent is directed to a hydrate of crystalline mupirocin calcium. The '155 patent is directed to anhydrous crystalline mupirocin calcium. The '093 patent is directed to a process for preparing crystalline mupirocin calcium or a hydrate thereof by “reacting pseudomonate ions with calcium ions in solution in an aqueous solvent, recovering a crystalline calcium pseudomonate hydrate from the solution and thereafter optionally removing water of crystallization.”
The Baker et al. patents disclose preparing amorphous form of mupirocin calcium by crystallization from an aqueous solution consisting of 50% methanol followed by trituration with dry ether. Amorphous mupirocin calcium obtained in the patents exhibits a relatively low melting point of 70-76° C., a relatively low assay of 89.9% (expressed as a percentage of pure free pseudomonic acid) and rapid deterioration at high temperatures (chart in Columns 8 and 9 of the '093 and related patents). The Baker et al. patents disclose that “the readily isolable amorphous form of this salt has been found to be sparingly water soluble material, having a low melting point and poor thermal stability.” (Column 1, Lines 31-33).
U.S. Pat. No. 4,639,534, incorporated herein by reference, discloses use of a lithium salt as an intermediate in isolating pseudomonic acid from a broth. The '534 patent extracts the broth to obtain mupirocin lithium and hydrolyzes the salt to obtain pseudomonic acid.
A need exists in the art to prepare mupirocin calcium dihydrate with new processes. Processes which eliminate the use of a co-solvent are particularly preferred in that removal of a co-solvent is a tedious step and may lead to deterioration of the product. A need also exists in the art for a process for preparing a more pure and stable form of amorphous mupirocin calcium.